(1) Field of the Invention
The present invention relates to the field of aviation and to providing assistance in the piloting of a rotary wing aircraft such as a helicopter. The invention relates more particularly to a safety system seeking to avoid an undesirable event such as colliding with the outside environment, and it is based on observing a reduction in the spread of paths available for a helicopter as a function of time. A helicopter fitted with such a safety system is safer since it makes it possible to limit the risks of an accident. In addition, such a helicopter can be remotely piloted, e.g. a drone, or it may carry a pilot and/or a crew.
The invention also relates to a method of limiting the risk of an accident during a helicopter flight, and when, unfortunately, a collision with terrain in relief or an obstacle cannot be avoided, such a method can serve to limit the consequences of such an accident.
(2) Description of Related Art
In general manner, known safety systems and methods for applications of this type do no more than evaluate a risk by making use of a database storing data associated with previous accidents. One such system is described in particular in Document U.S. Pat. No. 6,940,426.
Nevertheless, that type of safety system is ineffective when an undesirable event arises that is not listed in the database. Furthermore, undesirable events are often complex since they are the result of a string of several undesirable events contributing to degrading the current flight situation, or indeed in the worst case, leading to an accident of the helicopter. Unfortunately, it is not possible to identify and list all effects that might be produced by the various possible combinations of undesirable events leading up to an accident.
A first object of the invention is thus to provide a solution that is simple, reliable, and effective for identifying a risk of an accident and for attempting to avoid the accident.
Furthermore, as described in Document US 2002/0055809, it is also known to use the principle of fuzzy logic for evaluating risks that are a function of the current flight situation. Nevertheless, under such circumstances, the paths for avoiding the risk are standard predicted paths, i.e. paths that are already stored in a memory. Furthermore, those paths are followed while conserving the current speed of the helicopter and, under such circumstances, that can increase the risk of an accident, and in any event can fail to limit its consequences.
Likewise, and as described in Document EP 1 891 618, a method and a system for providing assistance in piloting a military transport airplane are known that make it possible automatically to follow an avoidance path on detecting a ground-air threat.
Nevertheless, under those circumstances, the avoidance paths are lateral paths at low altitude presenting at least one lateral turn and at least one limit slope in order to follow an avoidance path departing as much as possible from the initial path. Furthermore, the set of fallback paths for such an airplane is thus limited and does not require an advanced computer.
Thus, Document EP 1 891 618 does not disclose a system comprising a specific computer for generating a three-dimensional envelope of fallback paths, where the envelope is defined as being the set of positions that can be reached by a helicopter, and thus being much more complex and larger than the set of positions that can be reached by an airplane. Under no circumstances can such a computer propose fallback paths e.g. involving portions that are vertical and/or involving paths with braking, and at least paths without any lateral turning.
Likewise, Documents EP 1 369 665, EP 0 790 487, EP 1 517 211, US 2006/158350, and EP 1 832 850 describe various methods and systems for assisting the piloting of aircraft flying at low altitude in order to avoid collisions between an aircraft and the terrain over which it is flying. Those methods and systems then also make it possible to modify the flight path of an airplane automatically when an obstacle, such as a mountain, is identified on the current path of the airplane.
Nevertheless, none of the Documents EP 1 369 665, EP 0 790 487, EP 1 517 211, US 2006/158350, and EP 1 832 850 describes a safety system comprising simultaneously a specific computer as described above, an emergency member for warning that the number of fallback paths for the helicopter has decreased, and a control member for undertaking corrective piloting actions when the number of fallback paths drops even more.